Transistor-transistor logic

ABSTRACT

Transistor-transistor logic, wherein a PN junction is formed in the semiconductor substrate to assure a sufficient transient current to flow when the two transistors at the output stage become transiently &#39;&#39;&#39;&#39;on,&#39;&#39;&#39;&#39; said PN junction being reversely biased to exhibit a barrier capacitance and said capacitance being coupled in parallel with the circuit, thereby sufficient circuit operation and high reliability being obtained with a simple structure.

0 United States Patent 1 1 3,562,560

[72] Inventor Hiroyuki Osako [56] References Cited Yokuhama Japan UNITED STATES PATENTS P 754313 3,118,114 1 1964 Barditch 317 234x [221 PM 3,138,743 6/1964 Kilby 317/101 fi 12 3,174,112 3 1965 Stelmak 317/235x [731 3,189,798 6/1965 Benjamin 317/234 3,213,380 10/1965 Husher 317/235x 3 335 341 8/1967 Lin 317/235 x22 [32] Priority Aug. 23,1967 [33] Japan Primary Examiner-James D. Kallam [3 l 42/515,739 Attorney-Craig, Antonelli, Stewart & Hill ABSTRACT: Transistor-transistor logic, wherein a PN junc- [5 41 TRANSlSTOR'TFANSISTOR LOGIC tion is formed in the semiconductor substrate to assure a suffi- 8 Claims 4 Drawmg Figs cient transient current to flow when the two transistors at the [52] U.S. Cl. 307/303, output stage become transiently on," said PN junction being 307/213; 317/235 reversely biased to exhibit a barrier capacitance and said [5 l Int. Cl H03k 19/08 capacitance being coupled in parallel with the circuit, thereby [50] Field of Search 317/234, sufficient circuit operation and high reliability being obtained with a simple structure.

' PATENTEUFEB 9mm 3,562,560

FIG. 4 2/ N a Vac INVENTOR 1 0mm;

BY R

ATTORNEYS TRANSISTOR-TRANSISTOR LOGIC BACKGROUND OF THE INVENTION l.Field of the Invention This invention relates to an improved transistor-transistor logic.

2.Description of the Prior Art The development of the techniques of semiconductor electronics including transistor techniques as a major part thereof and the related techniques have motivated the invention and development of the present-day IC (integrated circuits). The technique of IC has been developed not only for the purpose of microminiaturization, but also because it has the possibility of remarkably enhancing economies, reliability, simplicity of manufacture and easiness of usage all of which are essential for industrial products. The IC technique can be applied to general electronic devices and now it is in practical use.

The advantage obtained by integrating digital circuits have already been made clear and include higher reliability due to a decrease in junction points, a reduction of weight, an increase in efficiency due to simplification of the system composition and the like. As integration of logic circuits, the integration of DCTL (Direct Coupled Transistor Logic), RTL (Resistor Transistor Logic), DTL(Diode Transistor Logic), 'I'TL (Transistor-Transistor Logic) and the like has already been put into practice. Among them, a TTL circuit is the most advanced saturation type digital IC, and has such properties as minimum power consumption, maximum speed, and maximum immunity to noise.

In a TTL circuit, two transistors at the output stage may become transiently on" simultaneously and then a transient current is allowed to flow through the transistors. In a conventional TIL circuit, however, since a sufiicient current cannot flow due to the impedance present at the line leading to the terminals of the 'ITL circuit, a potential drop occurs and a satisfactory circuit operation cannot be achieved.

SUMMARY OF THE INVENTION An object of this invention is to provide a 'I'I'L wherein said deficiency is obviated.

Another object of the invention is to provide a 'ITL which is simple in structure, capable of sufficient circuit operation and has a high reliability. BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a 'I'IL circuit diagram for the explanation of this invention;

FIG. 2 is a waveform diagram for the explanation of the TTL shown in FIG. 1;

FIG. 3 is a schematic diagram for the explanation of this invention; and

FIG. 4 is a sectional diagram of an embodiment of 'ITL according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Description will be made on a TIL hereinbelow. FIG. 1 shows a NAND circuit using 'I'IL. Q,-Q,, show transistors. Q, is a multiple emitter transistor and illustrated to have two emitters connected to the input terminals A and B. The connection point of the transistors Q, and Q, is connected to the output tenninal C. R,R,, indicate resistors, Vcc indicates a terminal connected to the power supply and GND indicates a grounding terminal.

The operation of the 111 shown in FIG. 1 will now be described. When the multiple emitter transistor Q, is in a eutoff state, i.e. when high level input signals are applied to the input terminals A and B, a current flows through a resistor R, to the base of the transistor 0,. Then the transistors Q and 0,, become on" and the level of the output terminal C becomes low. Meanwhile, when the transistor Q, is on or when at least one of the input terminals A and B is supplied with a lowlevel signal, the current from the power source terminal Vcc flows through the resistance R, and the base of the transistor 0, to the emitter of the transistor 0,. Accordingly the transistors Q and Q, are cutoff, the transistors O, and Q, are turned on" and a high-level signal is derived from the output terminal C. This behavior is show ig FIGS. 2(a) and (b), which show that the relation C {8:13 holds and the circuit described forms a NAND circuit.

The transient state of said operation will be described specifically with an attention to the level transition. When at least one of the input terminals A and B is supplied with a low level signal, the transistor 0 is on and the transistor Q, is cut off. When high-level signals are applied to both the ter minals A and B, the transistor 0 is cutofi and the transistor 0,, is on." Generally, on account of the characteristics of the transistors and the influence of the peripheral elements, the transition from the off state to the on" state occurs faster than the transition from the on state to the off state. Accordingly, the transistor Q, becomes cutoff with a time lag after the transistor 0,, becomes "on." Therefore, there occurs a state where both the transistors Q, and O are on" simultaneously. The same is true when the input signal is turned from a high-level to the low-level state and there occurs a transient state wherein the transistors Q and Q, are on" simultaneously. Due to said phenomena, a transient current Icc shown in FIG. 2(c)flows between the terminals Vcc and GND. However, such a rapidly changing current lcc cannot be supplied sufficiently due to the presence of the line impedance extending to the terminal Vcc. Thus the potential at the terminal Vcc drops and a satisfactory circuit performance may not be achieved. The following expedients are taken to eliminate said effect of the line impedance.

FIG. 3 shows the IC package 11, and the IC chip I2 is set substantially to the center thereof. In the IC chip 12, the TI'L circuit shown in FIG. I is formed. The package 11 comprises 14 pins each of which is connected to the relevant tenninal of the IC chip 12. The pins 13 are connected to the terminal Vcc shown in FIG. I and the pins I4 are connected to the terminal GND by means of the lines I5 and 16, respectively. In order to prevent the influence of the line impedance, the pin 13 corresponding to the terminal Vcc and the pin I4 corresponding to the terminal GND are coupled with a capacitor C,. According to this method the influence of the line impedance between the pins 13 and 14 can be eliminated, but the influence of the line impedance of the lines 15 and I6 in the package 11 cannot be removed. The influence of the line impedance of the lines 15 and I6 can be removed and the transient current lcc can be assured to flow if a capacitor C is inserted between the terminals Vcc and GND. However, it is impossible to couple such a capacitor to a very minute IC and said method has not been employed in the field.

According to this invention, this problem is solved by another method. Thus a sufficient Icc current is assured in a transient state and sufficient circuit operation is achieved.

FIG. 4 shows a sectional diagram of a 'ITL according to this invention, wherein the part of the transistor Q, is particularly magnified. The semiconductor substrate 24 is illustrated to have a P-type conductivity. An N-type impurity is diffused into the substrate 24 to form an N-type collector layer 21, a P- type impurity is diffused into the collector layer 21 to form a P-type base layer 22 and an N-type impurity is diffused into the base layer 22 to form N-type emitter layers 23. The substrate 24 comprises not only the transistor 0,, but also other circuit elements. Each element is provided with terminals and is connected to the other terminals by an appropriate method to compose a circuit.

Further, in order to assure the transient current to flow in the transient state, an N-type impurity is diffused into the substrate 24 to form an N-type layer 25. Most effective result was obtained when an N-type impurity was diffused into the back surface of the substrate 24. v

The substrate 24 is grounded by a GND terminal and the N- type layer 25 is connected to the power source terminal Vcc so that it may always be biased reversely. Thus the junction part 26 made between the P-type substrate 24 and the N-type layer 25 has an electrostatic capacitance on account of the barrier capacitance of said junction part 26. The semiconductor substrate is not limited to be of P-type. When the substrate is of N-type, a P-type impurity is diffused to form a P-type layer to give a barrier capacitance to the junction part. Namely, there is formed, in a substrate having one conductivity type, a layer having the conductivity type opposite to said one conductivity type to form a PN junction. When the PN junction is reversely biased, the junction part exhibits a barrier capacitance which is connected in parallel to a circuit such as shown in FIG. 1 to assure the transient current to flow.

Thereby, the transient current flowing through the circuit in the transient state is assured and a sufficient circuit operation can be achieved without lowering the potential at the terminal Vcc.

1 claim:

1. A transistor-transistor logic circuit comprising a semiconductor substrate having one conductivity type and a layer formed in said substrate and having the conductivity type opposite to said one conductivity type, said substrate and said layer forming a PN junction which exhibits a barrier capacitance when reversely biased, and said barrier capacitance being coupled in parallel to the circuit of the logic to assure a sufficient transient current to flow through the circuit.

2. A transistor-transistor logic circuit according to claim 1, wherein said layer is located at the back surface of said substrate.

3. An integrated circuit device comprising:

a semiconductor substrate of a first conductivity type;

a transistor-transistor logic circuit formed in said semiconductor substrate;

a semiconductor layer having a second conductivity type which is opposite to said first conductivity type formed in said substrate, wherein said layer and said substrate exhibit a barrier capacitance when reversely biased; and

means connecting said layer in parallel to the transistortransistor logic circuit.

4. The integrated circuit device of claim 3, wherein said semiconductor substrate has a first and a second principal surface, said first and second principal surfaces being on nonadjacent surfaces of the substrate wherein said transistortransistor logic circuit is formed in said first principal surface and said semiconductor layer is formed on said second principal surface.

5. The integrated circuit device of claim 4, wherein said first and second principal surfaces are substantially parallel.

6. The integrated circuit device of claim 3, wherein the substrate is connected to ground and the layer is connected to a power source.

7. The integrated circuit device of claim 3, wherein said substrate has a P-type conductivity and said layer has an N- type conductivity.

8. The integrated circuit device of claim 3, wherein said substrate has an N-type conductivity and said layer has a P- type conductivity. 

2. A transistor-transistor logic circuit according to claim 1, wherein said layer is located at the back surface of said substrate.
 3. An integrated circuit device comprising: a semiconductor substrate of a first conductivity type; a transistor-transistor logic circuit formed in said semiconductor substrate; a semiconductor layer having a second conductivity type which is opposite to said first conductivity type formed in said substrate, wherein said layer and said substrate exhibit a barrier capacitance when reversely biased; and means connecting said layer in parallel to the transistor-transistor logic circuit.
 4. The integrated circuit device of claim 3, wherein said semiconductor substrate has a first and a second principal surface, said first and second principal surfaces being on nonadjacent surfaces of the substrate wherein said transistor-transistor logic circuit is formed in said first principal surface and said semiconductor layer is formed on said second principal surface.
 5. The integrated Circuit device of claim 4, wherein said first and second principal surfaces are substantially parallel.
 6. The integrated circuit device of claim 3, wherein the substrate is connected to ground and the layer is connected to a power source.
 7. The integrated circuit device of claim 3, wherein said substrate has a P-type conductivity and said layer has an N-type conductivity.
 8. The integrated circuit device of claim 3, wherein said substrate has an N-type conductivity and said layer has a P-type conductivity. 